Sprinklers Above Gypboard Ceiling


I have a 29 x 72 mobile office with a 2-foot deep wooden truss above the ceiling that a client is required to sprinkler. Is there any way to avoid sprinklering above the gypboard ceiling?


Since this property is presumably already constructed, you're likely to have to remove the ceiling, giving you three choices: sprinkler the space, fill it with noncombustible insulation, or paint the trusses and wood deck with FR paint. These options are based on the information in NFPA 13, the sprinkler standard that likely applies to your structure. It includes the following exceptions for concealed spaces in what typically would be sprinklered areas (13:

• formed by studs or joists with less than 6" between edges.

• formed by bar joists with less than 6" between roof/floor and ceiling.

• formed by ceilings attached to or within 6" of wood joists.

• formed by ceilings directly attached to composite wood joists provided joist channel is fire-stopped into volumes not exceeding 160 ft3 with material equal to that of the webs.

entirely filled with non-combustible insulation. *

• within wood or composite joist construction with insulation filling space from ceiling to bottom of joist and in composite wood construction firestopped into volumes not exceeding 160 ft3 with material equal to that of the webs.

• over isolated small rooms not exceeding 55 ft2 in area.

created with rigid materials with any exposed surface having a flame spread rating of 25 or less.*

constructed entirely of fire-retardant treated wood as defined by NFPA 703. *

• noncombustible construction having exposed combustible insulation where the heat content of the facing and substrate does not exceed 1000 BTU/ft2.

• created by insulation laid directly on top of or within the ceiling joists in an otherwise sprinklered attic.

• a pipe chase under 12 ft2 formed by studs or wood joists, provided they are firestopped at each floor and contain no sources of ignition.

• exterior columns under 10 ft2 in area formed by studs or wood joist, supporting exterior canopies that are fully protected with a sprinkler system.

* applies to truss systems

For additional information on sprinkler systems with truss construction, see SBCA’s TTB – Sprinkler Systems & Wood Trusses.

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